This invention relates to improvements in and relating to filtering dust collectors.
Various dust collectors have been proposed and broadly in use especially for the prevention of atmospheric pollution. As an example, mechanical dust collectors such as, for instance, cyclones, venturiscrubbers and the like, and electrical dust collectors utilizing the ionization of the entrained dust particles, and further, bag filters and the like are now broadly being used in various industries for refining of gaseous media such as polluted atmosphere through removal of contained dust particles.
Among others, the filtering dust collector with filter material, preferably in the form of fibrous cloth, fine wire net and the like, is most advantageously utilized on account of its simpler structure, yet for its high operating efficiency, especially for removal of finer dust particles contained in the gaseous medium to be purified. With prolonged operation of such filtering dust collector, the collected dust particles will accumulate on the filtering surfaces of the filter per se, in the form of filter cake, so that the filter pores may be filled up substantially, thus increasing the pressure losses caused thereby. In order to avoid such pressure losses, giving rise to a substantially reduced filtering efficiency, frequent cleaning of the thus filled filter pores must be carried out by application of mechanical blows preferably at regular time intervals. Or alternatively, regular exchange of the filter material by new one must be performed. It is not only costly to execute such filter exchange, but also the filtering operation must be interrupted during such exchange job.
In order to avoid such difficulty, it has already been proposed to strike mechanically the filter material, preferably at regular time intervals for driving the accumulated particles of the filter. As an alternative measure, application of pulsative air streams or air jet streams against the filter is frequently employed for the same purpose in the conventional technique.
It is a common drawback inherent in the conventional techniques above referred to that the filter material is subjected to local severe stresses, as induced therein almost always in the repeated mode, which considerably reduces the durable life of the filter.
It is therefore the main object of the invention to provide a filtering dust collector operative, indeed, without invitation of localized and repeated substantial stresses in the filter material and capable or removing the accumulated dust particles therefrom in an efficient manner for substantial prevention of otherwise possible efficiency reduction of the filter, and indeed, with the benefit of an increased durable life of the filter material.
In order to fulfill the above main object, the improved filtering dust collector is characterized by the provision of a number of dust-repulsing electrodes which are provided in close proximity to or even embedded within the filter material, said electrodes being adapted for being impressed with a single phase or multi-phase high A.C. voltage. According to this invention, the gas streams entraining dust particles and therefore to be refined are passed normally and preliminarily through a nest of a plurality of sets of ionizing electrodes; each one electrode of one of said pairs is electrically connected with a high D.C. voltage source, while the other electrode of each of the electrode pair is earthed, so as to electrically charge or ionize the entrained dust particles. Then, the thus ionizing particles together with the entraining gas streams are passed through the filter material for separating the particles from the streams and depositing substantial part of the thus separated-off particles upon the upstream surface of the filter material. The thus refined gas streams are discharged from the outlet opening of the casing of the dust collector.
With progress of the filtering operation, the quantity of the separated and deposited dust particles will increase and finally they constitute a filter cake on the filter material, and the pressure loss thereat will increase correspondingly, thus the filtering efficiency being decreased correspondingly. For avoiding such disadvantage, the repulsing electrodes are switched on, preferably at properly selected regular time intervals or upon sensing the downstream side pressure drop by a certain predetermined value, so as to impress high A.C. voltage which may be preferably of a multi-phase, most preferably be of the three phase mode, as will be more fully described hereinafter. In this way, the filter cake is separated exclusively electrodynamically for regeneration of the filtering efficiency of the once clogged filtering pores or fine meshes.
After removal of the filter cake, the repulsing electrodes are again switched off.
In the case of the application of a multi-phase, preferably three phase A.C. high voltage energy, the repulsing electrodes are energized with the A.C. phase voltages in the successive order, so as to provide a progressive wave effect to be described.
It should be noted that the ionizing effect on the dust particle as applied during passage of the gas streams through the ionizing nest and as maintained during flow passage from the nest to the mechanical filter is brought about more specifically in such a way that the gas molecules are ionized and will be attached onto the overall surface of the dust particle which acts as if it be an ionized single molecule in its behavior.
Whe occasion desires, the ionizing electrodes nest can be replaced by an electric dust collector unit or units. In this way, coarser particles are caught by the electrostatic precipitator(s), while finer dust particles may be collected at the mechanical filter and then subjected to the electrodynamic repulsion by energization of the repulsing electrodes and upon deposited on the filter material of the mechanical filter.
In a preferred embodiment of the invention, the high A.C. voltage may be applied in the form of pulses.
A preliminary application of about 1,000 - 2,000 A.C. voltage can be, when necessary, applied to the repulsing electrodes, indeed, in advance of the main application of the regular A.C. high voltage thereto under consideration.
When a series of the dust-repulsing electrodes is applied with a single phase A.C. high voltage, an alternating electrical field is established between each two successive members of the electrodes, which field has a maximum buldge-out cross section at the center between these electrodes. Generally-speaking, each of these particles will move along the lines of force in the oscillating mode with the A.C. frequency. Therefore, the particle will be subjected to a combined influence of the thus generated coulomb force and the centrifugal force of different degree as determined by the occasionally occupying position by the particle along the line of force. Since the resultant force appearing in proximity to repulsing electrode is rather intense under substantial influence of the coulomb force, thus being subjected to a rather large repulsing force. On the other hand, at an intermediate point near the center point between the electrodes, the both kinds of the component forces are both effective substantially so that the subjected repulsing and resultant force becomes rather small. Anyhow, by application of a properly selected A.C. high voltage, such as 10,000 - 15,000 volts, as an example, the deposited filter cake can be removed effectively from the filter material overcoming the influence of the gas flows under treatment and the cohesive force among the particles constituting the cake. As was referred to hereinbefore, the filter material can perform the separation of the fouling dust particles from the gaseous medium and the electrical field may take charge of the prevention of formation of filter cake on the filter per se.
As was referred to, the single phase A.C. high voltage as impressed upon the repulsing electrodes can be used in the form of pulse voltages. In this way, the most predominant parts of the A.C. voltage energy can be utilized in an accentuated manner, so as to improve the operating efficiency so far.
When applied the dust-repulsing electrodes with a properly selected multi-phase A.C. voltage, a transmission force directing in the filter surface direction can be established; such force can be defined as the progressive wave effect.
This and further objects, features and advantages of the invention will become more apparent when read the following detailed description of the invention by reference to the accompanying drawings illustrative of several preferred embodiments of the invention.